Control device for forward and backward travel of automatic _pneumatic percussion boring devices

Abstract

A control device for working cycles of a self-propelled pneumatic boring device with a non-rotatable axially displaceable impact piston controllable by control edges of a control sleeve supported axially non-displaceably but rotatably and at its front end forming a control head with the control edges. The control head engaging in a cylindrical recess at a rear end of the impact piston cooperates with a radial main control opening formed in the impact piston in the vicinity of the recess. The control edges form two different pairs of the control edges, offset peripherally as well as axially such that respectively in one rotated position of the control sleeve only one of the pairs is aligned for cooperation with the main control opening. The impact piston is formed with at least one additional control opening which cooperates with the other pair and has a flow cross-section considerably smaller than that of the main control opening. The rear control edges of both of the pairs are formed in common by a rear circumferential edge of the control head.

I claim: 
     
       1. In a control device for two working cycles of forward movement and rearward movement respectively of a self-propelled pneumatic ram boring device with an impact piston which is axially displaceable forwardly and rearwardly in a control stroke between two abutments, respectively impacting one of the abutments in each working cycle, in a generally tubular-shaped housing, whereby the axial forward movement and rearward movement of the ram boring device is controllable by control edges of a control sleeve, the latter being supported non-displaceably in the axial direction however rotatably on a bearing ring arranged in a rear part of the tubular-shaped housing, said control sleeve being connected to a compressed air hose and through which compressed air is fed to the impact piston driving the latter in its axially displaceable forward and rearward movement, and which sleeve has at its front end a piston-shaped control head containing the control edges, the control head engaging in a cylindrical recess at a rear end of the impact piston cooperates with at least one radial control opening which is formed in the impact piston in the vicinity of the recess, the control edges forming two different types of pairs of the control edges, each of said pairs having a front said control edge and a rear said control edge, said two different types of pairs being offset in the peripheral direction as well as in the axial direction relative to each other such that respectively in one rotated position of said control sleeve during operation of the ram boring device in each one of the two working cycles, respectively, only one of said two different type of pairs of the control edges is aligned cooperating with the control opening and the other of the two different type of pairs is not aligned with and does not cooperate with the control opening, and said impact piston being guided non-rotatably in the housing, the improvement wherein 
     
     
       said control opening constitutes a main control opening, said impact piston is formed with at least one additional control opening which cooperates with said other pair of the control edges,   said at least one additional control opening has a flow cross-section considerably smaller than that of the main control opening, and   the rear control edges of both said pairs are formed in common by a rear circumferential edge of said control head.   
     
     
       2. The device as set forth in claim 1, wherein said main and said additional control openings are arranged in a common radial plane of the impact piston.   
     
     
       3. The device as set forth in claim 1, wherein said at least one additional control opening is staggered in axial direction with respect to the main control opening.   
     
     
       4. The device as set forth in claim 1, wherein the front control edge of the axially rearwardly offset pair is formed by a recess formed in and extending from a forward edge of the control head.   
     
     
       5. The device as set forth in claim 4, wherein the front control edge of the axially rearwardly offset pair has a first control edge section adapted to be aligned cooperating with the main control opening and a second control edge section adapted to be aligned cooperating with the additional control opening, respectively, said first and second control edge sections being staggered axially relative to each other.   
     
     
       6. The device as set forth in claim 1, wherein said at least one additional control opening is offset in the peripheral direction of the impact piston with respect to said main control opening. 
     
     
       7. The device as set forth in claim 1, wherein said rear circumferential edge of said control head forming said rear control edges of both said pairs is arranged in a common radial plane with respect to said control sleeve. 
     
     
       8. The device as set forth in claim 1, wherein said rear circumferential edge of said control head is circularly continuous. 
     
     
       9. The device as set forth in claim 1, including two of said at least one additional control opening offset in the peripheral direction substantially 180° relative to each other and two of said main control openings offset in the peripheral direction substantially 180° relative to each other, and two control edges of each said type of pairs disposed substantially 180° opposite each other. 
     
     
       10. The device as set forth in claim 1, including said at least one additional control opening is formed in the vicinity of said recess in the impact piston.